A gunman released the last two remaining hostages at an office building in Indiana and then shot himself twice in the head, police said today.

The suspected gunman was taken to a hospital in critical condition.

No hostages remain in the Prudential real estate office that a gunman ambushed today believing someone in the office owed him money, according to Sgt. Mike Grennes of the Valparaiso police department.

One woman suffered a head injury during the hostage situation but, aside from the suspected gunman, there were no injuries caused by gunshots, he said.

FBI agents entered the Valparaiso, Ind., real estate office building around 1 p.m. after a report of hearing gunshots fired, Grennes said. The gunman, whose identity was known to police, initially remained in the building with the hostages.

"We're basically in a standoff situation," Grennes said at a news conference before police said the gunman shot himself. "From what I understand, he is not an employee."

Authorities believed the incident could have been the result of a financial dispute, Grennes said.

Police received a 911 call around 11 a.m. from someone inside the Prudential Building that a gunman had entered the office, Grennes said. Police arrived and confirmed that an individual was inside with a gun.

Police were successful in getting some people out of the building, but they did not know the number of people left inside as the situation dragged on into the early afternoon hours.

Andy Melin, the superintendent of Valparaiso Community Schools, told ABC News that three schools in the area went on "a modified lockdown" when the situation began Friday morning. The three schools are Flint Lake Elementary School, Thomas Jefferson Elementary School, and Thomas Jefferson Middle School, all within "roughly a mile or a mile and a half of the Prudential Building," according to Melin.

"Everyone's on alert," Melin said. "There's an axe on the outer door and no one is allowed access to our building unless they are identified as an employee or parent."

Melin noted that a full-scale lockdown would be "something more imminent" such as "an intruder in the vicinity." In that case, Melin said, "students would be locked in their rooms and bigger security measures" would be in place.

"We will stay on a modified lockdown until the situation is resolved," Melin said, noting that the dismissal times for the schools were fast approaching.